The present invention relates to a construction for prevention of leakage of microwaves from the periphery of the door of a high frequency heating appliance and more particularly the invention is intended to achieve improved microwave leakage-preventive performance as well as cost reduction and to provide a light-weight door by minimizing the thickness of the door of the type in which a choke attenuator enters the oven cavity.
Conventionally, in high frequency heating appliances of the type additionally using electric heaters and having a pyrolytic self-cleaning function, it has been necessary during the cleaning function to raise the oven cavity temperature to about 500.degree. C., making it necessary to increase the thickness of the door, as compared with ordinary ovens, to improve the heat insulating performance of the door.
As for microwave seal-in constructions for this kind of oven, the one shown in FIG. 1, which is of the type in which a choke attenuator enters an oven cavity, is in wide use. With this construction, however, since a choke groove which is as long as 1/4 of the operating microwave wavelength, or about 30 mm, projects into the oven cavity, the effective size of the oven cavity is correspondingly decreased. Moreover, since the thickness of the door becomes quite large, the door itself is quite heavy and hence the door and the door support construction are expensive. A reduction in the size of the choke attenuator would reduce the door thickness, but with this measure alone the microwave seal-in performance would be degraded.